This invention relates to a pinless folder for a web offset printing press.
A pinless folder for a web offset printing press as shown in FIGS. 6 and 7 is known. In FIG. 6, the numeral 1 denotes a former. A web a folded in two by the former 1 (or an unfolded web b) is fed between a pair of first nipping rollers 2 and then between a pair of second nipping rollers 3. These nipping rollers rotate at the same peripheral speed as the travel speed of the web a. Then, the web a is fed to, and cut by, a cutting apparatus comprising a cutter cylinder 4 and a cutter bearing cylinder 5.
The cut paper (or signature) is rapidly speeded up by a pair of speedup transport belts 6, 6' guided by a pair of guide rollers 15, 15' to increase the distance between the trailing edge of a preceding sheet and the front end 18 of a succeeding sheet, and form a space S therebetween (see FIG. 7). Thus, the front end 18 of the succeeding sheet is gripped by grippers 8 of a folding cylinder 7 without undergoing interference by the trailing edge of the preceding sheet.
A middle part of the gripped succeeding sheet is pushed between a gripper board and a gripper pad of a gripping device 11 of a jaw cylinder 10 by a folding blade 9 of the folding cylinder 7 speeded up to the same peripheral speed as that of the speedup transport belts 6, 6'. As a result, the succeeding sheet is folded in two. The so folded succeeding sheet is then fed to a transport belt 12, a delivery fan wheel 13, and a delivery conveyor 14 in this order, and transported to the outside of the folder.
The above-described pinless folder poses the following problems:
(1) After the web a is cut, the cut sheet is rapidly increased in speed (by about 15-40%) to a level higher than the travel speed of the web a. Thus, a sheet end bend is apt to occur, especially, at both ends of the sheet which lie off the edges of the speedup transport belts 6, 6'. Furthermore, the sheet tends to incline, causing a disorder such as poor folding accuracy.
(2) The web a, sandwiched between the speedup transport belts 6, 6' and caused to slide while traveling, is suddenly fed (increased in speed) after trailing edge cutting. Thus, the front end position of the sheet fluctuates. It becomes difficult for the front end of the sheet to enter a predetermined grip position of the gripper 8. In this respect as well, folding accuracy is low.
(3) Before trailing edge cutting of the web a, the web a is caused to slide between the speedup transport belts 6, 6'. Thus, a printed pattern on the web a tends to be scratched by the belts.
(4) The web a is cut while being caused to slide between the speedup transport belts 6, 6'. After cutting, the sheet is transported while being sandwiched between the speedup transport belts 6, 6'. Thus, strict belt pressure adjustment is necessary. A lot of time and a high degree of skill are required for this task, lowering the operation rate of the folder.
(5) The web a is cut while being caused to slide between the speedup transport belts 6, 6'. Thus, static electricity tends to occur. If travel resistance due to static electricity is nonuniform in the width direction of the sheet, the sheet is twisted, and the fold is formed obliquely to the sheet end. Moreover, the posture and arrangement of sheets discharged to the delivery conveyor 14 are difficult to correct.
(6) The sheet guided by the speedup transport belts 6, 6' toward the folding cylinder 7 may be jammed between the speedup transport belts 6, 6'. Withdrawal of this sheet takes time. In this respect, too, the operation rate of the folder declines.
(7) The front end of the speeded up sheet is gripped by a plurality of grippers 8 arranged in a row in the sheet width direction of the folding cylinder 7 that has been speeded up to the speed of the sheet. Thus, bends tend to occur at both ends of the sheet lying off the grippers 8 positioned at both ends. A break can also happen owing to a buckle at the sheet end between adjacent grippers 8. Furthermore, the cut sheet is folded down the middle with the folding cylinder 7 and the jaw cylinder 10 being speeded up. Thus, the folding accuracy is prone to decline.
The foregoing phenomena (1) to (7) worsen as the folder operates at a higher speed.
A pinless folder as a solution to the above-described problems was proposed by Japanese Laid-Open Patent Publication No. 61705/95.
According to this pinless folder, as shown in FIG. 4, a web a folded in two by a former 1 is fed between a pair of first nipping rollers 2 and then between a pair of second nipping rollers 3. These nipping rollers rotate at the same peripheral speed as the travel speed of the web a. Then, the web a is fed between a first cutter cylinder 21 and a folding cylinder 23 so that interrupted cuts are formed in the web a in the paper width direction by a cutting apparatus comprising a cutter pad 34' of the folding cylinder 23 and saw blades 30 of the first cutter cylinder 21 see FIG. 5(a)!.
At this time, an around-the-cylinder transport belt 24 is moving in a circulating manner while contacting the outer peripheral surface of a lower part of the folding cylinder 23. Thus, the web a, interruptedly cut in the paper width direction, is sandwiched between the outer peripheral surface of the lower part of the folding cylinder 23 and the around-the-cylinder transport belt 24, and fed between a second cutter cylinder 26 and the folding cylinder 23. As a result, the remaining regions of the web a (the regions sandwiched between the respective thin belts of the around-the-cylinder transport belt 24) are cut in the paper width direction by a cutting apparatus comprising the cutter pad 34' of the folding cylinder 23 and saw blades 31 of the second cutter cylinder 26 see FIG. 5(b)!.
The front end of the web a, thus cut in the entire width, is pushed between grippers 32 attached to the folding cylinder 23 and gripper pads 33 attached to the folding cylinder 23 by a hold-down blade 28 of a front end hold-down cylinder 27 {the hold-down blade 28 notched at the front end in the paper width direction to avoid interference by the around-the-cylinder transport belt 24 see FIG. 5(c)!}.
In the vicinity of the side surface of the gripper pads 33 of the folding cylinder 23, there is nothing which interferes with the above action. Thus, the front end of the web a can be pushed, without difficulty, into the folding cylinder 23. When this front end is pushed in, each hold-down blade 28, each gripper 32, and each gripper pad 33 are arranged linearly in the same row in the axial direction of the folding cylinder 23. The front end of the web a pushed between the grippers 32 and the gripper pads 33 is gripped while being bent in the radial direction.
The web a gripped by the folding cylinder 23 is further rotated and moved together with the folding cylinder 23. The rear end (trailing edge) of the web a is cut by the second cutter cylinder 26 to separate a signature. The middle of the separated signature is inserted into a gripping device 11 of a jaw cylinder 10 by a folding blade 29 of the folding cylinder 23. At this time, the grippers 32 of the folding cylinder 23 gripping the front end of the signature are opened to fold the signature in two parallel to the cut surface. Then, the signature is fed to a transport belt 12, a delivery fan wheel 13, and a delivery conveyor 14 in this order, and transported to the outside of the folder.
The above folder obviates the need to make the web a slide between speedup transport belts as done in the aforementioned speedup single-stage pinless folder. Thus, no printing troubles, such as belt scratches, are caused to a printed pattern on the web a. Furthermore, static electricity occurs minimally, folding accuracy can be improved, and the posture of the sheet discharged onto the delivery conveyor 14 can be easily corrected. Nor is it necessary to speed up the web a by speedup transport belts. Thus, the belt pressure need not be adjusted, paper jam can be made practically nonexistent, and the operation rate can be improved.
The above-mentioned conventional pinless folder, however, involves the following problems:
(1) A cutting step is performed twice (two-stage cutting). Thus, the cut surface is irregular see FIG. 5(d)!. This can easily cause a paper jam in a subsequent step (delivery), and result in poor jogging in a stacker bundler.
(2) A phase adjustment mechanism may be constructed between the first and second cutting stages in order to avoid the irregularity of the cut surface. However, the adjustment of the cutting phase becomes necessary at the machine rise and the speedup, depending on a difference in the state of paper associated with the difference between low and high speeds, or a change in the movement of paper according to the change in the quality of paper. Thus, phase adjustment is tiresome and leads to much waste paper.
(3) Many component parts are involved, including the first cut-off cylinder, the second cut-off cylinder, and the front end hold-down cylinder. Thus, maintenance and management are tiresome, and the machine is upsized.